Anatomy, chloroplast structure and compartmentation of enzymes relative tophotosynthetic mechanisms in leaves and cotyledons of species in the tribeSalsoleae (Chenopodiaceae)

Certain members of the family Chenopodiaceae are the dominant species of th e deserts of Central Asia; many of them are succulent halophytes which exhi bit C-4-type CO2 fixation of the NAD- or NADP-ME (malic enzyme) subgroup. I n four C-4 species of the tribe Salsoleae, the Salsoloid-type Kranz anatomy in leaves or stems was studied in relation to the diversity in anatomy whi ch was found in cotyledons, Halocharis gossypina, has C-4 NAD-ME Salsoloid- type photosynthesis in leaves and C-3 photosynthesis in dorsoventral non-Kr anz cotyledons; Salsola laricina has C-4 NAD-ME Salsoloid-type leaves and C -4 NAD-ME Atriplicoid-type cotyledons; Haloxylon persicum, has C-4 NADP-ME Salsoloid-type green stems and C-3 isopalisade nonKranz cotyledons; and S, richteri has C-4 NADP-ME Salsoloid-type leaves and cotyledons. Immunolocali zation studies on Rubisco showed strong labelling in bundle sheath cells of leaves and cotyledons of organs having Kranz anatomy. The C-4 pathway enzy me phosphoenolpyruvate carboxylase was localized in mesophyll cells, while the malic enzymes were localized in bundle sheath cells of Kranz-type tissu e. Immunolocalization by electron microscopy showed NAD-ME is in mitochondr ia while NADP-ME is in chloroplasts of bundle sheath cells in the respectiv e C-4 types, In some C-4 organs, it was apparent that subepidermal cells an d water storage cells also contain some chloroplasts which have Rubisco, st ore starch, and thus perform C-3 photosynthesis. In non-Kranz cotyledons of Halocharis gossypina and Haloxylon persicum, Rubisco was found in chloropl asts of both palisade and spongy mesophyll cells with the heaviest labellin g in the layers of palisade cells, whereas C-4 pathway proteins were low or undetectable. The pattern of starch accumulation correlated with the local ization of Rubisco, being highest in the bundle sheath cells and lowest in the mesophyll cells of organs having Kranz anatomy. In NAD-ME-type Kranz or gans (leaves and cotyledons of S. laricina and leaves of H, gossypina) the granal index (length of appressed membranes as a percentage of total length of all membranes) of bundle sheath chloroplasts is 1.5 to 2.5 times higher than that of mesophyll chloroplasts, In contrast, in the NADP-ME-type Kran z organs (S. richteri leaves and cotyledons and H, persicum stems) the gran al index of mesophyll chloroplasts is 1.5 to 2.2 times that of the bundle s heath chloroplasts, The mechanism of photosynthesis in these species is dis cussed in relation to structural differences.